1. Field of the Invention
The invention relates to a throttle valve control mechanism for an engine and more particularly to a throttle valve control mechanism that is most suitable to an engine of an outboard motor.
2. Description of Related Art
Recently, some outboard motors incline to utilize four stroke engines. One reason for this tendency is that emissions from the four stroke engines are clean rather than those of two stroke crankcase compression engines. An engine for an outboard motor generally has a single cylinder bore or multiple cylinder bores extending generally horizontally in its engine body. Also an air induction system is provided for introducing air charge to the single or multiple combustion chamber(s) in the engine body. Usually, the air induction system for a four stroke engine has a single or multiple air intake duct(s) extending generally horizontally along the cylinder bore(s) and a common plenum chamber placed upstream of the air intake duct(s). It is desirable to make the air intake ducts proper lengths for improving engine power, particularly the torque characteristic under acceleration conditions from low or medium speeds by using the inertia charge effect.
In the meantime, conventionally a throttle valve for admitting air charge to the combustion chamber(s) is contained in a throttle body placed upstream of the plenum chamber. Due to this arrangement, the length(s) between the throttle valve and the combustion chamber(s) tend to be relatively long. Thus, the engine cannot response so quickly to the operator""s desire. Accordingly, the operator is likely to have bad feeling in engine operation. In order to shorten the length(s) as much as possible, it can be proposed to dispose the throttle valve within the (each) throttle duct.
If the engine has only a single cylinder, a throttle valve control mechanism of the throttle valve could be relatively simple. However, if multiple cylinders are provided, the control mechanism would be somewhat complicated. In addition to that, the engine is encircled with a protective cowling and there is only narrow space between the engine body and the protective cowling. Under the circumstances, it is a problem how to dispose a throttle valve control mechanism in this narrow space. This problem comes up not only to a four stroke engine but also to, for example, a two stroke crankcase compression engine if, for example, such an engine has an air intake duct extending between an engine body and a protective cowling.
It is, therefore, a principal object of this invention to provide a multiple cylinder engine wherein a throttle valve control mechanism is suitably provided in space between an engine body and a protective cowling.
Also, an engine for an outboard motor is quite often operated at a fixed engine speed within a low or medium speed range. Thus, it is desirable to make the throttle valve control insensitive at this speed range so that the operator can keep the engine speed in the generally fixed state easily. Another engine may require another characteristic in the throttle valve control.
It is, therefore, another object of this invention to provide an engine wherein a throttle valve control mechanism can have various control characteristics.
In accordance with one aspect of this invention, an internal combustion engine comprises a plurality of generally horizontally extending bores having their axis spaced vertically relative to each other. A plurality of pistons are provided and each piston reciprocates within a respective one of the cylinder bores. A cylinder head closes one end of the cylinder bores. Each of the cylinder bores, the pistons and the cylinder head generally defines a respective combustion chamber for burning an intake charge. An air induction system communicates with the combustion chambers for supplying at least air charge thereto. The air induction system includes a plurality of air intake ducts. Each of the air intake ducts has a throttle valve for admitting the air charge to the combustion chamber. Each of the throttle valves has a valve shaft which axis extends generally vertically. Respective throttle valves are linked together. Means are provided for controlling the throttle valves. The throttle valve control means have an actuator being movable in a plane existing generally horizontally for rotating the valve shafts about each axis so that the openings of the throttle valves are controlled. Almost of the other part of the throttle valve control means are movable in a plane existing generally vertically.
In accordance with another aspect of this invention, an internal combustion engine comprises an engine body having at least one cylinder. The cylinder includes a cylinder bore, a piston reciprocating within the cylinder bore and a cylinder head closing the cylinder bore. The cylinder bore, the piston and the cylinder head generally defines a combustion chamber for burning intake charge. The engine further comprises an air induction system for supplying at least air charge to the combustion chamber. The air induction system includes a throttle valve for admitting the air charge to the combustion chamber. The throttle valve has a valve shaft around which the throttle valve rotates. Means are provided for rotating the valve shaft non-linearly as compared with an input operation thereof.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.